Basic Ionization Research Articles

USE AND ADVANCEMENT OF ANALYTICAL AND INSTRUMENTATION SYSTEMS: TWO-DIMENSIONAL GEL ELECTROPHORESIS, ELECTROSPRAY IONIZATION, MATRIX ASSISTED LASER

Gel electrophoresis is a technique which is used for the separation purpose and its applications are in pharmaceuticals, in health especially in cancer detection. Matrix assisted laser ionization is also a technique which is used for crude oil refinement and also used for protein separation. Electrospray ionization is a technique in which it works as a combination with the mass spectrometry. And it has more reproducibility. Electrospray also has both the acidic and basic ionization modes.

Integrated Quantum Mechanical and Machine Learning Methods Enable Scalable and General pKa Prediction for Pharmacokinetic Modeling

We present the development of the BIOiSIM™ pKa model for predicting aqueous molecular ionization. Assessment and optimization of drug pKa occurs early in drug discovery; thus, models for high‐throughput pKa prediction must balance computational cost, scalability, accuracy, and applicability to diverse chemical structures. Key to our pKa prediction model is a set of low computational cost, quantum mechanical charge descriptors that incorporate not only ionizable group charges, but the additional atoms and bonds likely to modulate pKa. The finalized machine learning models produced good accuracy on the test holdout set (R2 = 0.9, mean absolute error = 0.6−0.7, root mean square error = 1.0) and show good generalizability predicting the most acidic and basic ionization centers of the SAMPL6 external benchmark validation set (mean absolute error = 0.8, root mean square error = 1.0). Performance of the model is comparable to commercial pKa predictors but is trained on less data and exhibits higher scalability needed for pharmacokinetic modeling.

Prediction of fraction unbound in plasma in children in data-limited scenarios for human health risk assessment

In human health risk assessment, pediatric physiologically-based pharmacokinetic modeling has been used to predict chemical-specific toxicokinetic adjustment factors. An important input parameter fraction unbound in plasma in child (fupchild) can be scaled from fupadult using ontogeny models. Multiple computational tools can be used to predict fupchild for data-poor compounds but prediction accuracy can be different depending on data-availability. We evaluated prediction of fupchild for data-limited scenario with data-rich compounds. The objectives were (i) to evaluate the uncertainty of the ontogeny models in different data availability scenarios and (ii) to evaluate how these different data availabilities can impact the overall prediction accuracy of fupchild. Six calculation methods that emulate various data-availability scenarios were applied to calculate 139 fupchild values. The ionization state at pH 7.4 and QSPR-predicted fupadult values were calculated from the structure of a molecule using ADMET Predictor. When the albumin ontogeny equation was applied to calculate fupchild for all compounds, fupchild values were under-predicted compared to observed fupchild with average fold error (AFE) values from 0.68 to 0.74. When the AAG model was used, a less degree of bias was observed. When the binding partner was assumed based on acid-base properties, the prediction accuracy was similar to the cases where fupchild values were calculated based on known binding partner information. When QSPR-predicted fupadult values were used as an input, substantial over-predictions were observed for acids and neutrals with an AFE up to 8. The results demonstrated that an experimental determination of fupadult was crucial and prediction of acidic or basic ionization status at pH 7.4 was sufficient to select the most appropriate ontogeny model that could predict fupchild from fupadult.

Magnet stage optimization of 5 kW multi-cusped field thruster

The multi-cusped field thruster is a unique electric thruster device, which has many advantages such as long lifetime, large-range thrust throttling ability, high thrust density, and low mass. The thruster employs several alternating polarity permanent magnets to create a periodic magnetic field with several cusps. Previous studies have indicated that the basic ionization and acceleration processes are directly related to the electron motion behavior, which mainly depends on the magnetic field characteristics. The magnet number and magnet stage length are two key magnetic field parameters that have important effects on the thruster performances. In this paper, both the magnet number and magnet stage length parameters are studied for the optimization of a 5 kW multi-cusped field thruster. The results indicate that the three-stage thruster has a better electron confinement than the two-stage thruster. It has lower ion energy loss at the wall, and shows a higher ionization rate. Therefore, the three-stage magnetic field is a superior magnetic field configuration. Besides, the three-stage magnetic field simulation results indicate that an optimal accelerating electric field distribution and ionization region distribution could be obtained when the magnet length ratio is 78:25:20.

A dielectric and spectrophotometric study of the tautomerization of 2-hydroxypyridine and 2-mercaptopyridine in water

The basic ionization (pk1) and acidic ionization (pk2) constants and equilibrium constant (KT) of 2HPy and 2MPy were determined. The pk1(s) of their N- and X-methyl derivatives (X = O, S) were also determined. The equilibrium constant of 2MPy is approximately 60 times greater than its oxygen analog, 2HPy. The micro-ionization constants of the functional groups, –NH (pkA and pkC) and –XH (pkB and pkD), were determined to provide further insights into the ionization equilibria of these N-heteroaromatic XH compounds (2HPy and 2MPy). The relaxation time of water (τ) in aqueous solutions of 2HPy and 2MPy are collectively used with the KT values to determine the forward (kf) and backward (kb) rate constants of tautomerization. Subsequently, the kf and kb are used to provide the rationale for the KT and τ values.

Modeling the Impact of pH- and Oxygen-Coupled Stimuli on Osmotic Pressure and Electrical Potential Responses of Hemoglobin-Loaded Polyampholyte Hydrogel.

A unique character of (bio) responsive materials is their capability to convert specific environmental biochemical cues into an electromechanical response. Thereby, this paper describes the impact of pH- and oxygen-coupled stimuli on osmotic pressure and electrical potential responses of hemoglobin-loaded polyampholyte hydrogel. Herein, a multiphysics model is developed for elucidating the multiphysical interaction between immobile functional components bounded onto polymeric network chains of the hydrogel and hydrogen ion-oxygen-enriched environmental solution. Two constitutive relationships are incorporated into the model to capture: (1) ionization of fixed charge group as a function of its ionization strength coupled with hydrogen ion concentration and (2) bioactivity of hemoglobin as a function of both its ionization and saturation states. The multiphysics model is verified by comparing with experimental observations in open-literature, capturing the oxygen-induced hemoglobin saturation and the pH-actuated deformation of polyampholyte hydrogel. The numerical finding demonstrates that the pH-activated osmotic pressure response of the present hemoglobin-loaded polymeric system is independent of ambient oxygen O2, whereas its electrical potential response is insensitive of ambient oxygen O2 level at pH neutral conditions. Furthermore, the pH-induced swelling deformation of initially balanced polyampholyte hydrogel changes from a "V-" to a "bowl"-shaped like pattern with increase in fixed acidic and basic group ionization strength, whereas the initially unbalanced polyampholyte hydrogel achieves a collapse state at environmental pH coinciding with acid-base dissociation constant of dominant immobile charge group, if the initial dominant immobile charge group density is twice that of its counter one.

Improving the selectivity and sensitivity for quantifying 8-α-hydroxy-mutilin in rabbit tissues by using basic mobile phases and negative ionization.

Previously reported LC-MS methods for quantifying 8-α-hydroxy-mutilin (a marker residue of tiamulin) in tissues all used a pseudo MRM transition (from protonated molecular ion to protonated molecular ion, m/z 337→337) due to difficulties in finding a product ion, leading to suboptimal selectivity and sensitivity for detection. By using electrospray negative ionization in a basic medium, we, for the first time, found a highly selective and sensitive true MRM transition for 8-α-hydroxy-mutilin, m/z 335→179. With this newly found MRM transition and the use of pleuromutilin as the internal standard, a very sensitive, selective, and robust LC-MS/MS method has been developed and validated for quantifying 8-α-hydroxy-mutilin in rabbit tissues (muscle, liver, kidney, and fat). In comparison with the previously published methods, the selectivity and sensitivity were significantly improved. For the concentration range validated (0.2-10ppm or 0.2-10μg/g), the within-run and between-run accuracies (% bias) ranged from -5.0 to 3.1 and -4.9 to 3.0, respectively. The% CV ranged from 2.2 to 6.6 and 4.7 to 8.3 for within-run and between-run precisions, respectively. The validated method was successfully used to support two GLP tissue residue depletion studies in rabbits.

Determination of Ionizing Radiation Exposure Levels within Four Local Mining Sites Selected from Sardauna Local Government Area of Taraba State - Nigeria

Miners and the people living close to mining sites are exposed to elevated levels of ionizing radiation with or without their consent. This study determined the background ionizing radiation of four mining sites from Sardauna local government area of Taraba state using an inspector alert nuclear radiation meter manufactured by S.E. International, Inc USA with serial number 35440. The meter has a halogen- quenched Geiger Muller tube with a ± 45 mm effective diameter and mica window density of 1.5- 2.0 mg/cm3. The Geiger tube in the meter generates a pulse of electrical current each time radiation is incident on the tube and causes ionization. The measured values ranged from 0.19 - 0.40 mSv/yr across all the mining sites and 500 m away from the sites. These results were found to be far less than the standard of 1.0 mSv/yr set by International Commission on Radiological Protection (ICRP) for the general public and 20.0 mSv/yr set by the Nigeria Basic Ionization Radiation Regulation (NiBIRR) for the whole body of adult radiation protection workers which means that the miners and inhabitants of this areas are safe. Nevertheless, there could be long term variations in the consequences arising from the effects of ionizing radiation among the miners and even the inhabitants. Strong correlations were found between the equivalent doses at the excavating and the processing points of the sites which mean that the miners and people living close to these mining sites are subjected to uniform distribution of consequences arising from ionizing radiation. We do recommend that policy makers and regulatory bodies should apply mitigation measures to the effects by means of creating awareness to the miners at various mining sites and the use of modern mining strategies to protect other natural resources especially water.

Effect of CO2 and natural surfactant of crude oil on the dynamic interfacial tensions during carbonated water flooding: Experimental and modeling investigation

Carbonated water has been recently proposed as an enhanced oil recovery method for crude oil reservoirs. Interfacial tension (IFT) plays a crucial rule on the displacement of trapped oil ganglia in the porous media. This investigation is designed to systematically assess the dynamic interfacial tension (DIFT) of two different types of crude oils with carbonated water (CW). In addition, the measured experimental data were applied into specified models. The DIFT behavior of acidic and non-acidic crude oil samples/CW and deionized water (DW) are also compared to find the effect of dissolved carbon dioxide in water on IFT. At the next stage, DIFT of all the results were used through three different models namely diffusion-controlled, mono-exponential models and an empirical equation. In this way, induction, adsorption (i.e. relaxation or rapid fall), equilibrium and meso equilibrium times, diffusivity of surface active materials in the crude oil to the crude oil/aqueous phase interface (DSA) and surface excess concentration of surface active components (ГSA) of CW systems are calculated and compared with those of the crude oil-DW systems.While IFT reduction is considered as an effective mechanism of CW injection for more oil recovery, the obtained results in the current investigation show a contradicting trend. In details, the dissolved CO2 reduces the pH of the aqueous phase, consequently, increases the basic natural surfactant ionization. The obtained results show that domination of ГSA reduction compared to the ionization of basic natural surfactant leads to IFT enhancement.

Influence of substituents structure and their electronic effects on acid-base and complexing properties of 5,10,15,20-tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin

5,10,15,20-Tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin has been prepared, and its acid-basic properties have been studied in acetonitrile by titration with 1,8-diazabicyclo [5.4.0]undec-7-ene and perchloric acid. The substituted porphyrin ability towards complex formation with zinc acetate has been studied in acetonitrile and acetonitrile, 1,8-diazabicyclo [5.4.0]undec-7-ene media. Spectral properties of neutral and ionic forms of 5,10,15,20-tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin and its zinc complex have been determined; constants of acid and basic ionization of the ligand have been estimated. Kinetic parameters of the porphyrin complex formation with zinc via molecular and ionic mechanism have been analyzed. The substituents effect on the studied properties is discussed.

Origin of energetic carbon ions with different charge states in ultrashort laser-thin foil interactions

High charge state carbon ions are observed from the rear surface of thin foil irradiated by intense femtosecond laser pulse at intensities up to 6.4×1018 W/cm2. The origin of the ions is studied by analyzing the basic ionization process occurring at the rear surface. It is shown that the normally dominant ionization process is field ionization by barrier suppression for charge states less than He-like (C4+), while collisional ionization is significant for C5+ and C6+.

Morphology of nanoscale structures on fused silica surfaces from interaction with temporally tailored femtosecond pulses

Laser control of two basic ionization processes on fused silica, i.e., multiphoton ionization and avalanche ionization, with temporally asymmetric pulse envelopes is investigated. Control leads to different final electron densities/energies as the direct temporal intensity profile and the time inverted intensity profile address the two ionization processes in a different fashion. This results in observed different thresholds for material modification on the surface as well as in reproducible lateral structures being an order of magnitude below the diffraction limit (down and below 100 nm at a numerical aperture of 0.5). In this contribution, the morphology of the resulting structures is discussed.

Differential study on molecular suppressed ionization in intense linearly and circularly polarized laser fields

We present a differential study on above-threshold ionization of the O{sub 2} (N{sub 2}) molecule as well as the companion atom Xe (Ar) (with close ionization potential) produced by linearly and circularly polarized laser fields (25 fs, 795 nm). The photoelectron angular distributions of the companion target are similar at the same laser condition. In both linearly and circularly polarized fields, we observe that the photoelectron yields of O{sub 2} are suppressed in the entire energy spectral range as compared with Xe with fully differential measurements, but not for the N{sub 2}-Ar pair. This is different from the prediction of photoelectron energy spectra by the model including the interference terms [Phys. Rev. Lett. 85, 2280 (2000)], from which the low-energy photoelectrons of O{sub 2} were expected to be strongly suppressed in both linearly and circularly polarized laser fields. Resorting to the basic strong-field ionization picture, we believe that the lower orbital-dependent multiphoton excitation or tunneling possibility of O{sub 2} as compared with Xe is responsible for this effect. High-resolution fully differential data pose a stringent test on the current strong-field calculations on molecules.

Control of Ionization Processes in High Band Gap Materials

An overview on femtosecond laser pulse shaping techniques applied to control of the initial photo-physical steps involved in materials processing is presented. First, pulse shaping methodology in frequency domain is introduced and examples of shaped pulses relevant to laser microfabrication are discussed. Then, the use of tailored femtosecond pulses to control the initial steps of laser processing of high band gap materials is demonstrated. In particular, control on basic ionization proc-esses acting as the initial photo-physical step of the ablation dynamics is exerted by highly asymmetric femtosecond laser pulse shapes generated by Third Order Dispersion (TOD).

Townsend coefficient, escape curve, and efficiency of runaway-electron beam formation in argon

The ionization and drift characteristics of electrons in argon are simulated by the method of multi-particle dynamics. It is shown that, in argon (as well as in other gases studied earlier), the Townsend regime of ionization sets in even in strong fields if the electrode distance is much larger than the reciprocal Townsend coefficient. The dependences of the basic ionization and drift characteristics on the reduced field intensity are obtained, and an escape curve is constructed separating the region of effective electron multiplication from the region where the electrons leave the discharge gap having no time to multiply. The formation efficiency of a runaway-electron beam is calculated. It is shown that the dependence of the electrode voltage generating a given fraction of runaway electrons on the product of the pressure by the electrode distance has a form that qualitatively agrees with the runaway curve. When the efficiency is not too high (≤20%), the runaway curves virtually coincide with isoefficiency curves.

Control of ionization processes in high band gap materials via tailored femtosecond pulses

Control of two basic ionization processes in dielectrics i.e. photo ionization and electron-electron impact ionization on intrinsic time and intensity scales is investigated experimentally and theoretically. Temporally asymmetric femtosecond pulses of identical fluence, spectrum and pulse duration result in different final free electron densities. We found that an asymmetric pulse and its time reversed counterpart address two ionization processes in a different fashion. This results in the observation of different thresholds for surface material modification in sapphire and fused silica. We conclude that control of ionization processes with tailored femtosecond pulses is suitable for robust manipulation of breakdown and thus control of the initial steps of laser processing of high band gap materials.

Townsend coefficient and efficiency of the formation of runaway electrons in neon

Basic ionization and drift properties are simulated for neon by the method of multiparticle dynamics. This calculation revealed that, in neon—in just the same way as in other gases that were studied previously—the Townsend ionization regime is realized even in strong fields if the distance between electrodes is rather large. The dependences of basic ionization and drift properties on the reduced electric-field strength are obtained. The results agree with available experimental data. The escape curve separating the region of efficient electron multiplication from the region in which electrons leave the discharge gap without undergoing multiplication is found for neon. The efficiency of the formation of a runaway-electron beam in helium and neon is simulated.

PH Dependence of the reaction catalyzed by avian mitochondrial phosphoenolpyruvate carboxykinase.

The pH dependence of the reaction catalyzed by phosphoenolpyruvate carboxykinase (PEPCK) provides significant insight into the chemical mechanism. The pH dependence of k(cat) shows the importance of two acidic ionizations with pK(a) values of 6.5 and 7.0 assigned to the active site metal ligands H249 and K228. A single basic ionization is observed with an apparent pK(a) value of 8.4 that is assigned to K275 that is located in the P-loop motif and is essential for phosphoryl transfer. The pH dependence of k(cat)/K(M,PEP) demonstrates the importance of the same two acidic ionizations in the interaction of phosphoenolpyruvate with PEPCK and a single basic ionization with a pK(a) value of 8.1 that is assigned to Y220. The interaction of Mg-IDP with PEPCK is dependent upon a single acidic ionization attributed to K228 and two basic ionizations, both having an average pK(a) value of 8.1. One of the basic ionizations is attributed to the P-loop lysine (K275) and the other to C273.

PH of simple ampholytes and related compounds. A general, always‐converging, iterative algorithm

For the aqueous solutions of those electrolytes whose acid‐base behaviour is completely described by only one acid andonly one basic ionization process, a new, original, iterative algorithm for the calculation of their pH values is derived from the exact, electroneutrality equations, in a unitary fashion, although these electrolytes belong to different classes. The fact that this algorithm always converges to the root of these equations is given a qualitative proof.

Chemical Reactivity and Basicity of Amines Modulated by Micellar Solutions

The kinetics of the reactions of several secondary aliphatic amines with alkyl nitrites (2-bromoethyl and 1-phenylethyl nitrites) weee measured using the spectrophotometric technique in aqueous basic solutions and in the presence of sodium dodecyl sulfate and tetradecyltrimethylarnmonium bromide. In the case of the cationic micelles, the results were quantitatively interpreted by means of the pseudophase model, which considers micelles acting as a separate phase from water. With the anionic micelles, the results weee analyzed by using the simple pseudophase ion-exchange model, in which the alkyl nitrite and the neutral form of the amine are partitioned between the micellar and aqueous pseudophases, and in which the basic ionization equilibria of the amine increases because of the exchange between the alkylammonium ion of the amine and the micellar counterion at the micellar surface. Bimolecular rate constants for the reaction in the micellar pseudophase are always smaller than for those in water. Characteristic features of the media and of the substrates in the reactivity behavior of amines are discussed. The binding constants of the amines (by hydrophobic or electrostatic effects) to the micelle are seen as related to the structure of the amine and the nature of the micellar surface. © 1995, American Chemical Society. All rights reserved.